1,721,132 research outputs found
A New Procedure for Optimal Design of District Metered Areas Based on the Multilevel Balancing and Refinement Algorithm
No full textA procedure for optimal design of District Metered Areas (DMAs) within a water distribution network based on a multilevel balancing and refinement algorithm to partition the network and determine the optimal meter positions, coupled with a pressure driven hydraulic simulator to quantify the hydraulic performance of the districtualized system, is presented.
Unlike other procedures based on graph partitioning techniques proposed in the scientific literature, the two main issues involved in the design of the DMAs, namely a) how to partition the nodes into the required number of districts, and b) which pipes linking districts to leave open, and fitted with an assigned number of flow meters, and which to close, are simultaneously resolved.
The application of this procedure to a real case shows that this approach provides design solutions well adapted to different numbers of measuring points, yielding superior performance indicator values to similar procedures reported in the literature and used here for comparative purposes
A Methodology for Pumping Control Based on Time Variable Trigger Levels
No full textAbstractA methodology for the control of a pumping plant feeding a tank is presented. This methodology is aimed at minimizing the energy costs by maximizing pumping during off-peak electricity tariff periods. It is based on trigger levels which are variable during the day according to a prefixed pattern in order to ensure that the water level in the elevated tank is at its minimum and maximum values at the end of the peak and off-peak tariff periods respectively. The pattern of the trigger levels is defined by solving a multi-objective problem aimed at minimizing the energy costs and the number of pump switches.The methodology was applied to the real case of a pumping plant feeding an elevated tank for daily balance which, in turn, feeds a small town in northern Italy; one week of hourly observed total consumptions was considered. This methodology was compared with other two methodologies typically used for pump control, i.e. pump scheduling and fixed trigger levels. The results show that the proposed methodology allows for achieving energy costs that are definitively lower than those obtainable by using fixed trigger levels, and comparable with those obtainable by using pump scheduling, being the number of pump switches the same. On the other hand, unlike the pump scheduling, the methodology presented does not require any water demand forecast and scheduling optimization to be repeated daily, thus representing an effective and efficient tool for pumping plant operation
Near optimal rehabilitation scheduling of water distribution systems based on a multi-objective genetic algorithm
No full textAn increase in breakage frequency and a decrease in system efficiency are observed when pipes become older. Rehabilitation strategies are necessary to face this problem in order to define when, where and how to operate for renewing the pipe system. These strategies are constrained by the amount of funds which are usually available not in a single instalment but yearly and spread over a time period of several years. A procedure based on a multi-objective genetic algorithm to search for a near optimal rehabilitation scheduling is proposed. With reference to a fixed time horizon, the goal is to minimise the overall costs of repairing and/or replacing pipes, and to maximize the hydraulic performances of the water network; the constraints are represented by the maximum costs which are allowed yearly, over a pre-selected time spell. A head-driven hydraulic simulator is linked to the optimizer to represent the different hydraulic and breakage scenarios which become possible in consequence of the rehabilitation schedules generated by the genetic algorithm. Results regarding a simple case study and a real water distribution system show that the proposed procedure has the potential to be a useful tool for rehabilitation scheduling
Rating curve uncertainty effects on extreme discharge frequency analysis evaluated through a grey-based technique
No full textA grey-based technique for characterizing both the rating curve uncertainty due to discharge measurement errors and its effect on flood frequency analysis is here presented.
On the basis of river stage measurements (affected by negligible errors) and corresponding discharge measurements (affected by uncertainty here represented through grey numbers) made in a gauged section, the grey parameters of the rating curve are estimated by using a grey non-linear regression. The rating curve with grey parameters can be interpreted both (a) as a grey function which provides an uncertain (grey) estimation of the discharge for a given river stage and (b) as a sheaf of crisp rating curves whose crisp parameters are included within the corresponding grey parameters. Given a set of annual maximum stages observed in the section, the frequency distribution (here assumed of EV1 type) of the annual maximum grey discharges is thus estimated through two approaches consistent with the two interpretations of the rating curve, i.e. exploiting the definition of grey function a) of the grey discharges and b) of the rating curve grey parameters.
The application of the methodology proposed to the data pertaining to a gauged section of the river Po (Italy) shows that the first approach yields a wider grey EV1 distribution with respect to that resulting from the second approach; this is due to the fact that, unlike the former, the latter explicitly takes into account the hydraulic consistency between discharges associated with different stages
Un modello di previsione in tempo reale della richiesta idrica nelle reti di distribuzione di acqua potabile
No full textIn questa memoria viene descritto un modello per la previsione in tempo reale delle richieste idriche orarie su di un intervallo temporale di 24 ore in avanti rispetto all’ora corrente. Esso ha una struttura modulare; il primo modulo consente la stima della richiesta idrica media giornaliera nel giorno (o nei giorni) interessati dalle 24 ore di previsione tenendo conto della ciclicità stagionale e settimanale delle richieste idriche giornaliere e della loro persistenza a breve termine. Analogamente, il secondo modulo consente la stima delle richieste idriche nelle 24 ore successive all’ora corrente, tenendo conto della loro ciclicità giornaliera e della persistenza a breve termine. L’analisi dei risultati ottenuti in relazione alle serie temporali osservate a Castelfranco Emilia (MO), a partire dalle quali il modello è stato strutturato, evidenzia che il modello è in grado di fornire una previsione accurata e robusta grazie alla rappresentazione dei comportamenti periodici e alla correzione fornita dalle componenti di persistenza. La validità della formulazione proposta è stata verificata anche in riferimento a serie temporali delle richieste idriche delle reti di distribuzione di Valencia (Spagna) e Haifa (Israele) le quali hanno caratteristiche molto diverse da quelle di Castelfranco Emilia
A heuristic procedure for the automatic creation of district metered areas in water distribution systems
No full textThis paper presents a procedure for the automatic creation of district metered areas (DMAs) in a water distribution system. The procedure uses techniques derived from graph theory (Breadth First Search and algorithm for finding the shortest paths in a graph) and demand-driven hydraulic simulations of the network in order to (a) divide the nodes among an assigned number of DMAs, (b) identify the “open” links between districts where flow meters will be placed and (c) identify the “closed” links between districts where isolation valves will be placed. The application of the proposed procedure to the case of a real water distribution system revealed it to be robust and effective. In particular, the results obtained show that the procedure makes it possible to identify very good solutions in terms of resilience and minimum pressures when reference to the peak demand and fire-flow conditions is made. The resulting performance indicators were better than those obtainable by applying a similar procedure previously proposed in the scientific literature
Assessment of predictive uncertainty within the framework of water demand forecasting using the Model Conditional Processor (MCP)
No full textThis paper presents an application of the Model Conditional Processor (MCP), originally proposed by Todini (2008) within the hydrological framework, to assess the predictive uncertainty in water demand forecasting related to water distribution systems. The MCP enables us to assess the probability distribution of the future water demand conditional on the forecasts provided by two or more deterministic forecasting models. In the numerical application described here, where two years of hourly water demand data for a town in northern Italy are considered, two forecasting models are applied in order to forecast hourly water demands from 1 to 24 hours ahead: the first model has a modular structure comprising a periodic component which reflects the long-term effects and a persistence component which represents the short-term memory of the process; the latter is based on neural networks. The results highlight the effectiveness of the approach, provided that the data set used for the MCP parameterization is properly selected so as to be actually representative of the accuracy of the real-time water demand forecasting models
Pianificazione degli interventi di riabilitazione su di una rete acquedottistica mediante algoritmi genetici multi-obiettivo
No full textIn questa memoria viene presentata una procedura per la pianificazione degli interventi di manutenzione di una rete di distribuzione acquedottistica. Con essa si intende definire la sequenza ottimale degli interventi da effettuarsi entro una predefinita finestra temporale, al fine di massimizzare, da un lato, l’affidabilità della rete e, dall’altro, di minimizzare il totale di tutti i costi. Viene inoltre imposto il vincolo che ogni anno la spesa totale non superi un assegnato valore. Le tecniche di intervento considerate sono la sostituzione con una nuova condotta di diametro commerciale uguale o superiore all’esistente e la pulizia (“cleaning”) della condotta stessa. Per valutare l’affidabilità della rete a fronte delle soluzioni proposte dall’ottimizzatore di tipo genetico viene utilizzato un simulatore idraulico di tipo “head-driven”. L’affidabilità della rete è quantificata sia in senso meccanico (capacità di far fronte agli eventi di rottura delle condotte), sia in senso idraulico (capacità di far fronte sia all’incremento nel tempo della resistenza delle condotte, sia alla variazione nel tempo delle richieste idriche). I risultati relativi ad un caso studio dimostrano le potenzialità della procedura proposta nel contesto della pianificazione degli interventi di manutenzione
A grey-based method for evaluating the effects of rating curve uncertainty on frequency analysis of annual maxima
No full textA grey-based technique for characterizing the rating curve uncertainty due to discharge measurement errors and its effect on flood frequency analysis is here presented.
On the basis of river stage and discharge measurements, the grey parameters of the rating curve are estimated by using a grey non-linear regression. Commencing with this grey rating curve and a set of annual maximum stages, we show how the probability distribution (here assumed of EV1 type) of the grey annual maximum discharges can be estimated.
The grey EV1 distribution can be estimated through two approaches, the first of which directly exploits the grey discharges corresponding to the annual maximum stages, whereas with the second approach two different sets of extreme (crisp) discharges, and therefore two EV1 distributions of extreme (crisp) values which delimit the grey discharges of a given return period, are obtained by considering the lower and upper limits of the grey parameters of the rating curve.
The methodology is illustrated using data pertaining to a gauged section of the river Po (Italy). The results show that the first approach yields a wider grey EV1 distribution with respect to that resulting from the second approach: physical justification of this is given
Una procedura per la distrettualizzazione delle reti di distribuzione idriche
No full textNella memoria si presenta una procedura per la distrettualizzazione automatica delle reti di distribuzione idrica. La procedura utilizza tecniche derivate dalla teoria dei grafi (ricerca in ampiezza dei nodi e calcolo dei percorsi di minima distanza) e simulazioni idrauliche della rete per a)ripartire i nodi tra un assegnato numero di distretti idrici e b) identificare quali tratti di collegamento tra i distretti lasciare aperti, al fine di massimizzare la resilienza della rete distrettualizzata.
L’applicazione della procedura a una rete reale ne evidenzia l’efficacia, fornendo valori dell’indice di resilienza e della pressione minima nella rete distrettualizzata leggermente migliori di quelli che si otterrebbero mediante una procedura di distrettualizzazione già disponibile nella letteratura scientifica
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